Viruses that infect bacteria are among the most abundant life forms on Earth. Indeed, our oceans, soils and potentially even our bodies would be overrun with bacteria were it not for bacteria-eating viruses, called bacteriophages, that keep the microbial balance of ecological niches in check. Now, a new study suggests that bacteriophages made of RNA likely play a much larger role in shaping the bacterial makeup of worldwide habitats than previously recognized.